Shadows are not continuous and only when i go near they be shown.

Hello...I am making a car game and i have a problem...When i drive the car the shadows of the mountains and the grass are not shown up from far distance.But when i drive they are created intime beside my car.How can i make them to been shown from very far distance?And if its easy i want to know why my car is flying on air.I took the script and the wheels from CarTutorial on Unity site,i just change the body. Here is an Web Example of my game: carunity.tk